Integrated test target assembly and compact collimator

Abstract

An improved wide-spectrum test target assembly, with visual and near IR (infrared) targets integrated with a long wavelength emissivity target. A single relatively thick optical fiber (78) is used to receive target signals emitting from several thinner fibers (72, 74, 76), each carrying a signal of different wavelength. The integrated signal is then relayed to an aperture (108) of an emissivity target through a gradient index lens (88) to further combine with the long wavelength target signal emitted from the emissivity target assembly (100). By selecting appropriate numerical apertures and diameters of the fibers, relatively high power output is achieved. A light collimator (200) is also disclosed for collimating light generated by the test target assembly to simulate targets at infinity. The collimator includes a primary mirror (220) which is an off-axis section of a paraboloidal mirror, a secondary mirror (230) which is an off-axis section of a hyperboloidal mirror, and a support structure/baffle (210) which supports the mirrors in proper relation and also includes an integrated light baffle surface to prevent light from the test target assembly from passing directly to an image plane.

What is claimed is: 
     
       1. A wide-spectrum integrated test target assembly for providing a plurality of test targets at a plurality of wavelengths, comprising: a plurality of light emitting diodes (LEDs) operating at different wavelengths for producing respective LED light outputs;   a plurality of relatively thin input optical fibers for conducting light emitted by said respective LEDs, said input fibers having a low numerical aperture (NA) characteristic;   a single, relatively thick output multimode optical fiber having an output face, said output fiber having a low NA characteristic;   direct optical coupling means for directly coupling said LED light conducted by said plurality of input optical fibers into said output optical fiber, wherein output faces of said input optical fibers are in optical contact with an input face of said output fiber;   said output fiber having a length sufficient to achieve pulse spreading of LED light from said LEDs and provide uniform optical energy distribution at said output face of said output fiber;   a target assembly comprising a glass substrate and a target defining layer disposed thereon, said target assembly further comprising a target aperture, wherein said glass substrate has a thickness dimension at said aperture, and wherein said thickness dimension of said substrate is much larger than a lateral dimension of said target aperture; and   means for optically relaying light emitted from said output face of said output optical fiber to said target aperture to increase angular spread of said light emitted at said output face, said optical relaying means including a lens.   
     
     
       2. The assembly of claim 1 wherein diameters defined by said LED connecting optical fibers are smaller than a diameter defined by said output fiber, said optical coupling means comprising means for holding ends of said LED optical fibers tightly together. 
     
     
       3. The assembly of claim 2 wherein said holding means comprises a first ferrule having an inner diameter sufficient to receive ends of said LED connecting fibers, a second ferrule having an inner diameter sufficient to receive an end of said output fiber therein, said ferrules having substantially equal outer diameters, and means for butting said ferrules together. 
     
     
       4. The assembly of claim 3 wherein said butting means comprises a sleeve having an inner diameter equal to said ferrule outer diameter, said ferrules being received therein. 
     
     
       5. The assembly of claim 1 wherein said plurality of LEDs comprise first, second and third LEDs respectively capable of emitting light at visible, first near infrared and second near infrared wavelengths. 
     
     
       6. The assembly of claim 1 wherein said optical relaying means further comprises an optical spacer element inserted between said output face of said output fiber and said lens. 
     
     
       7. The assembly of claim 6 wherein said lens is a gradient index lens having a flat input face, and wherein said output face of said output fiber is flat and perpendicular to said output fiber, and said spacer has flat input and output surfaces, and wherein said flat input surface of said spacer is butted against said output face of said output fiber, and said flat output face of said spacer is butted against said flat input face of said lens. 
     
     
       8. The assembly of claim 1 wherein said lens comprises a gradient index lens. 
     
     
       9. The assembly of claim 1 wherein said length of said output optical fiber is at least one meter. 
     
     
       10. The assembly of claim 1 wherein said input fibers have an NA equal to 0.22, and a nominal diameter dimension of 100 μm. 
     
     
       11. The assembly of claim 1 wherein said output fiber has an NA equal to 0.22, and a nominal diameter dimension of 300 μm. 
     
     
       12. A wide-spectrum integrated test target assembly for providing visible, near-IR and far-IR test targets, comprising: first, second and third light emitting diodes (LEDs) operating respectively at wavelength desired for producing visible and near-IR light outputs;   first, second and third relatively thin input optical fibers for conducting light emitted by said respective LEDs, said input fibers having a low numerical aperture (NA) characteristic;   a single, relatively thick output optical fiber having an output face, said output fiber having a low NA characteristic;   direct optical coupling means for directly coupling said LED light conducted by said first, second and third input optical fibers into said output optical fiber, wherein output faces of said input optical fibers are in optical contact with an input face of said output fiber;   said output fiber having a length sufficient to achieve pulse spreading of LED light from said LEDs and provide uniform optical energy distribution at said output face of said output fiber;   a target assembly comprising a glass substrate and a target defining layer disposed on a front face of said substrate, said target assembly further comprising a target aperture through which said visible, near-IR and far-IR test targets illuminate, wherein said glass substrate has a thickness dimension at said aperture, and wherein said thickness dimension of said substrate is much larger than a lateral dimension of said target aperture; and   means for optically relaying light emitted from said output face of said output optical fiber to said target aperture to increase angular spread of said light emitted at said output face, said optical relaying means including a gradient index lens.   
     
     
       13. The assembly of claim 12 wherein diameters defined by said LED connecting optical fibers are smaller than a diameter defined by said output fiber, said coupler comprising means for holding ends of said LED optical fibers tightly together. 
     
     
       14. The assembly of claim 13 wherein said holding means comprises a first ferrule having an inner diameter sufficient to receive ends of said input optical fibers, a second ferrule having an inner diameter sufficient to receive an end of said output fiber therein, said ferrules having substantially equal outer diameters, and means for butting said ferrules together. 
     
     
       15. The assembly of claim 14 wherein said butting means comprises a sleeve having an inner diameter equal to said ferrule outer diameter, said ferrules being received therein. 
     
     
       16. The assembly of claim 12 wherein said optical relaying means further comprises an optical spacer element inserted between said output face of said output fiber and said lens. 
     
     
       17. The assembly of claim 16 wherein said gradient index lens has a flat input face, and wherein said output face of said output fiber is flat and perpendicular to said output fiber, and said spacer has flat input and output surfaces, and wherein said flat input surface of said spacer is butted against said output face of said output fiber, and said flat output face of said spacer is butted against said flat input face of said lens. 
     
     
       18. The assembly of claim 12 wherein said length of said output optical fiber is at least one meter. 
     
     
       19. The assembly of claim 12 wherein said input fibers have an NA equal to 0.22, and a nominal diameter dimension of 100 μm. 
     
     
       20. The assembly of claim 12 wherein said output fiber has an NA equal to 0.22, and a nominal diameter dimension of 300 μm. 
     
     
       21. A multi-spectral test target system, comprising: a wide-spectrum integrated test target assembly for providing a plurality of test targets at a plurality of wavelengths, comprising: a plurality of light emitting diodes (LEDs) operating at different wavelengths for producing respective LED light outputs;   a plurality of relatively thin input optical fibers for conducting light emitted by said respective LEDs, said input fibers having a low numerical aperture (NA) characteristic;   a single, relatively thick output multimode optical fiber having an output face, said output fiber having a low NA characteristic;   direct optical coupling means for directly coupling said LED light conducted by said plurality of input optical fibers into said output optical fiber, wherein output faces of said input optical fibers are in optical contact with an input face of said output fiber;     said output fiber having a length sufficient to achieve pulse spreading of LED light from said LEDs and provide uniform optical energy distribution at said output face of said output fiber; a target assembly comprising a glass substrate and a target defining layer disposed on a front face of said substrate, said target assembly further comprising a target aperture, wherein said glass substrate has a thickness dimension at said aperture, and wherein said thickness dimension of said substrate is much larger than a lateral dimension of said target aperture; and   means for optically relaying light emitted from said output face of said output optical fiber to said target aperture to increase angular spread of said light emitted at said output face, said optical relaying means including a lens; and     collimating means for collimating said light relayed to said target aperture so as to simulate targets at infinity.   
     
     
       22. The system of claim 21 wherein diameters defined by said LED connecting optical fibers are smaller than a diameter defined by said output fiber, said coupler comprising means for holding ends of said LED optical fibers tightly together. 
     
     
       23. The system of claim 22 wherein said holding means comprises a first ferrule having an inner diameter sufficient to receive ends of said LED connecting fibers, a second ferrule having an inner diameter sufficient to receive an end of said output fiber therein, said ferrules having substantially equal outer diameters, and means for butting said ferrules together. 
     
     
       24. The system of claim 23 wherein said butting means comprises a sleeve having an inner diameter equal to said ferrule outer diameter, said ferrules being received therein. 
     
     
       25. The system of claim 21 wherein said plurality of LEDs comprise first, second and third LEDs respectively capable of emitting light at visible, a first infrared and a second infrared wavelengths. 
     
     
       26. The system of claim 21 wherein said optical relaying means further comprises an optical spacer element inserted between said output face of said output fiber and said lens. 
     
     
       27. The assembly of claim 26 wherein said lens is a gradient index lens having a flat input face, and wherein said output face of said output fiber is flat and perpendicular to said output fiber, and said spacer has flat input and output surfaces, and wherein said flat input surface of said spacer is butted against said output face of said output fiber, and said flat output face of said spacer is butted against said flat input face of said lens. 
     
     
       28. The system of claim 21 wherein said lens comprises a gradient index lens. 
     
     
       29. The assembly of claim 21 wherein said length of said output optical fiber is at least one meter. 
     
     
       30. The assembly of claim 21 wherein said input fibers have an NA equal to 0.22, and a nominal diameter dimension of 100 μm. 
     
     
       31. The assembly of claim 21 wherein said output fiber has an NA equal to 0.22, and a nominal diameter dimension of 300 μm.